1. Field of the Invention
The present invention relates to a method of manufacturing an outer race for a constant velocity universal joint of a tripod type, mainly for automotive use, by the utilization of a plastic working process and, more particularly, to the method of the kind referred to, wherein a chamfered area of a peripheral lip region of an opening is subjected to the plastic working process.
2. Description of the Prior Art
The constant velocity universal joint of the tripod type generally includes an outer race having a cup body formed with three track grooves, an inner race positioned inside the outer race, and rolling elements intervening between the outer and inner races in operative engagement with the associated track grooves. In this type of the constant velocity universal joint, assuming that the outer and inner races are rotating in unison with each other, a shaft coupled with the inner race can undergo a rocking motion relative to the outer race while pivoting about the center of pivot defined within the inner race. In order to avoid the possibility of the shaft interfering with a peripheral lip region of the cup body during the rotation thereof, one end of each of reduced diameter portions defined between the neighboring track grooves adjacent the peripheral lip region of the cup body is chamfered to provide a respective chamfered portion.
While the chamfered portions are generally defined by the use of a cutting process, the use of the cutting process is undesirable in terms of productivity and yield of production. For this reason, the use of a plastic working technique to define the chamfered portions is desirable. The outer race making method including a plastic working process to form the chamfered portions is disclosed in, for example, the Japanese Laid-open Patent Publication No. 2000-61576.
According to the above mentioned publication, an intermediate member which eventually forms the outer race is prepared by means of a combined pushing process including a forward pushing and a rearward container pushing, to thereby form a cup portion and, during this cup forming process, the chamfered portions are plastically formed by the use of a punch used to form the track grooves. Thereafter, during the subsequent drawing process to form the outer race to have a final design dimension and shape, the chamfered portions are also finished.
However, since the chamfered portions are formed during the cup forming process, the punch used to form the cup portion is required to have a complicated shape wherein. Specifically, the punch must be stepped so that a tapered peripheral surface area that eventually defines the chamfered portions can be formed at a portion of the punch intermediate of the length thereof. Since the punch for formation of the cup portion is one of elements of a mold used to define the track grooves and the reduced diameter portion between the neighboring track grooves, such punch has a relatively complicated shape. Accordingly, if the tapered surface area referred to above is formed to render the punch to represent a stepped configuration, the punch is indeed complicated considerably in shape. For this reason, the punch for formation of the cup portion will become difficult to manufacture and, more over, once such punch is worn down, repair thereof is difficult to achieve. By way of example, if when the punch is worn down the punch is desired to be repaired by removing a worn end portion thereof, the tapered area must also be repaired, making it difficult to repair the punch.